1. Field of the Invention
The present invention relates to a tunable capacitor and method of fabricating the same. More particularly, the present invention relates to a MEMS tunable capacitor with a wide tuning range and method of fabricating the same.
2. Description of the Related Art
As micromachining technology is developed, a micro-electromechanical system (MEMS) tunable capacitor that can replace a varactor diode used for frequency tuning is sought. While varactor diodes are simple and robust, they have a limited tuning range.
A conventional tunable MEMS capacitor includes a fixed charge plate and a movable charge plate. The movable charge plate is positioned above the fixed charge plate, and moves up and down due to application of an electrostatic force. A stiffener is positioned on the movable charge plate. The stiffener prevents the movable charge plate from bending when the movable charge plate moves down.
The tunable capacitor having the stiffener has a wider tuning range than a varactor diode. Since the movable charge plate of the tunable capacitor may be moved up and down by application of an electrostatic force, a distance between the fixed charge plate and the movable charge plate may be varied, thus varying the capacitance. However, a distance that the movable charge plate may move up and down is limited due to a short circuit and an electrostatic force between the plates. As a result, the tuning range of this MEMS tunable capacitor is still limited. In other words, a variable capacitor in which the capacitance is varied by moving the movable charge plate up and down still has a limited tuning range.